Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Ag-Pt”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Porous Interlayers that Getter Surface-Segregating Species for Improved Silver Wetting, Adhesion, and Electrical Contact on Stainless Steel SOFC Components

Here, porous nickel interlayers or porous platinum interlayers were shown to promote the wetting, spreading, and adhesion of silver on alumina-forming ferritic stainless steel (AFFSS) and chromia-forming ferritic stainless steel (CFFSS). These interlayers resulted in dense, crack-free AFFSS|Ag-Ni|CFFSS and AFFSS|Ag-Pt|CFFSS braze joints that, after 300 h in 650 °C air, displayed shear strengths up to 70 MPa similar to, or larger than, those of AFFSS|Ag-CuO|CFFSS or AFFSS|Ag|CFFSS joints subjected to identical treatment. Similarly, after exposure to 25 cycles of (50 switches between) 12 h of 650 °C air and 12 h of 650 °C 4%H 2 –96%N 2 , AFFSS|Ag-Ni|CFFSS and AFFSS|Ag-Pt|CFFSS braze joints displayed shear strengths significantly larger than those of AFFSS|Ag-CuO|CFFSS or AFFSS|Ag|CFFSS joints subjected to identical treatment. In addition, nickel and platinum were found to chemically getter surface-segregating steel constituents, particularly Al from the AFFSS. As a result, Ag-Ni and Ag-Pt electrical contact resistances on AFFSS and CFFSS substrates were several orders of magnitude lower than those of conventional Ag-CuO reactive air brazes or Heraeus C8710 Ag contact pastes. Together, these results suggest that Ag-Pt and especially Ag-Ni may be useful for the fabrication of durable joints, seals, and/or electrical contacts in electrical/electrochemical devices exposed to high temperatures and/or variable oxygen partial pressure environments.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Density Functional Tight Binding Insights into Plasmonic Silver–Platinum Nanoparticles and Alloys for Enhanced Photocatalysis

Developing accurate and efficient Slater-Koster (SK) tight-binding parameter sets is essential for quantum plasmonic studies of alloyed metal nanoparticles, as conventional time dependent density functional theory (TD-DFT) calculations are computationally prohibitive for larger clusters. In this work, we develop and validate density functional tight binding (DFTB) parameter sets for both ground state (GS-SK) and excited state (ES-SK) calculations to study the structural, electronic, and optical properties of silver (Ag), platinum (Pt), and Ag–Pt nanoalloys. Our investigation of the ground state properties demonstrates that the GS-SK parameters enable DFTB to closely reproduce the electronic structures of platinum clusters with diverse sizes and geometries – showing qualitative agreement with DFT for density of states (DOS) profiles and energy levels. The ES-SK parameters accurately describe excited-state properties compared to TD-DFT reference calculations, including the broad, featureless absorption profiles of Pt that are dominated by interband transitions. Using the ES-SK parameters within a real-time TD-DFTB framework, we compute size-dependent optical absorption spectra of Ag, Pt and Ag-Pt nanocubes containing up to 1099 atoms (size ∼4.18 nm). A detailed study of Ag–Pt and Pt-Ag core–shell nanoparticles shows quenching of the Ag plasmon resonance even at monolayer coverage for Ag-Pt, but not for Pt-Ag. We also show how to define submonolayer Ag-core Pt-shell cubic structures that have similar optical properties to those generated experimentally for much larger particles, which offers potential for describing plasmon-enhanced photocatalysis. Collectively, the GS-SK and ES-SK parameter sets provide an accurate, computationally efficient approach for modeling the complex optical and electronic behavior of noble–transition metal nanostructures and their alloys.

SPR↗
DOE OSTI2022

Effect of applied potential on metal surfaces: Surface energy, Wulff shape and charge distribution

Here we use grand canonical density functional theory to predict the surface energies, Wulff shapes, charge distributions and catalytically active sites of different metal surfaces under electrochemical conditions. We propose a method for computing surface energies from grand canonical density functional theory (GC-DFT) calculations of periodic slab models and use it to compute the surface energies of the facets of Pt, Cu, and Ag crystals to predict their Wulff shapes under electrochemical conditions. GC-DFT predicts that, for the pure metals studied, solvation only slightly affects the Wulff shape while applied potentials considerably affect the surface energies and corresponding Wulff shapes. We used Bader charge analysis of GC-DFT computed electron densities to investigate the effect of applied potential on the distribution of electron density over the atoms of the surfaces of Pt, Cu, Ag, and the 75–25 Ag-Pt and Au-Ni alloys. This analysis shows that, under an applied potential, the electron density is unevenly distributed over the surface atoms and that the charges of atoms more exposed to solvent are more sensitive to bias. Our results show that the most sensitive atom to bias can be used to identify the most favorable adsorption site and thus, the active sites of electrochemical reactions, which is computationally less demanding than calculating the adsorption energies on all possible adsorption sites.

36 MATERIALS SCIENCE↗
DOE OSTI2021

In-operando surface-sensitive probing of electrochemical reactions on nanoparticle electrocatalysts: Spectroscopic characterization of reaction intermediates and elementary steps of oxygen reduction reaction on Pt

In this paper we present an in-operando spectroscopic study of the reaction intermediates involved in ORR on electrified Pt nanoparticle electrocatalysts. To accomplish this, we have synthesized Ag-Pt core–shell nanoparticles, that contain a thin shell of Pt (~1 nm) uniformly deposited on a larger Ag core (~60 nm). We show that these nanostructures are ideal platforms for in-operando Plasmon Enhanced Raman Spectroscopy (PERS) of ORR on Pt. We combined these PERS studies with DFT calculations to assign the measured vibrational spectra to relevant surface intermediates as a function of electrocatalyst potential. Overall, these vibrational assignments were further verified and validated by performing PERS measurements using de-oxygenated and heavy oxygen (O 2 -18) saturated electrolyte. These studies allowed us to identity the presence of critical reaction intermediates (OH, O 2 , OOH, and H 2 O) as the function of operating voltage on the Pt surface and derive voltage-dependent elementary step mechanisms of the reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Structure and ultrafast dynamics of tri-nuclear Ag-/Tl–Pt 2 POP 4 complexes in solution

The energetics and dynamics of ion assembly in solution has broad influence in nanomaterials and inorganic synthesis. To investigate the fundamental processes involved, we present a time-resolved x-ray solution scattering (TR-XSS) study of the trinuclear silver and thallium complexes of the diplatinum ion PtPOP [Pt 2 (H 2 P 2 O 5 )$_4^{4−}$] in aqueous solution. These complexes, their structural properties, and their electronic structure are not well understood and afford a unique opportunity to study the metal–metal bond formation that influences molecular and material assembly in solution. We present model-independent analysis of the observed dynamics as well as an analysis incorporating time-resolved structural refinements of key bond lengths with $<$100 fs time resolution. We find that upon photoexcitation, the Pt atoms contract ∼0.25 Å toward the center of both the Ag- and the Tl-PtPOP complexes, as previously observed for the PtPOP anion. For the AgPtPOP system, an ultrafast Ag-Pt bond expansion of ∼0.2 Å is observed, whereas in contrast, the TlPtPOP system exhibits a Tl-Pt bond contraction of ∼0.3 Å upon photoexcitation. For both complexes, the change in electronic state leads to coherent (“wave-packet”) oscillations along the metal–Pt coordinates. Based on these structural dynamics, we propose an electronic structure model that describes the metal–metal bonding behavior in both the ground and excited state for both complexes.

Lenzen, Philipp [Technical Univ. of Denmark, Lyngb↗
DOE OSTI2020

Materials Data on Ag3Pt by Materials Project

PtAg3 is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Pt is bonded to twelve equivalent Ag atoms to form PtAg12 cuboctahedra that share corners with twelve equivalent PtAg12 cuboctahedra, edges with twenty-four equivalent AgAg8Pt4 cuboctahedra, faces with six equivalent PtAg12 cuboctahedra, and faces with twelve equivalent AgAg8Pt4 cuboctahedra. All Pt–Ag bond lengths are 2.90 Å. Ag is bonded to four equivalent Pt and eight equivalent Ag atoms to form AgAg8Pt4 cuboctahedra that share corners with twelve equivalent AgAg8Pt4 cuboctahedra, edges with eight equivalent PtAg12 cuboctahedra, edges with sixteen equivalent AgAg8Pt4 cuboctahedra, faces with four equivalent PtAg12 cuboctahedra, and faces with fourteen equivalent AgAg8Pt4 cuboctahedra. All Ag–Ag bond lengths are 2.90 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgPt3 by Materials Project

Pt3Ag is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Pt+0.67- is bonded to eight equivalent Pt+0.67- and four equivalent Ag2+ atoms to form PtAg4Pt8 cuboctahedra that share corners with twelve equivalent PtAg4Pt8 cuboctahedra, edges with eight equivalent AgPt12 cuboctahedra, edges with sixteen equivalent PtAg4Pt8 cuboctahedra, faces with four equivalent AgPt12 cuboctahedra, and faces with fourteen equivalent PtAg4Pt8 cuboctahedra. All Pt–Pt bond lengths are 2.83 Å. All Pt–Ag bond lengths are 2.83 Å. Ag2+ is bonded to twelve equivalent Pt+0.67- atoms to form AgPt12 cuboctahedra that share corners with twelve equivalent AgPt12 cuboctahedra, edges with twenty-four equivalent PtAg4Pt8 cuboctahedra, faces with six equivalent AgPt12 cuboctahedra, and faces with twelve equivalent PtAg4Pt8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgPt by Materials Project

PtAg crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Pt2- is bonded to six equivalent Pt2- and six equivalent Ag2+ atoms to form PtAg6Pt6 cuboctahedra that share corners with eighteen equivalent PtAg6Pt6 cuboctahedra, edges with six equivalent PtAg6Pt6 cuboctahedra, edges with twelve equivalent AgAg6Pt6 cuboctahedra, faces with eight equivalent PtAg6Pt6 cuboctahedra, and faces with twelve equivalent AgAg6Pt6 cuboctahedra. All Pt–Pt bond lengths are 2.83 Å. All Pt–Ag bond lengths are 2.90 Å. Ag2+ is bonded to six equivalent Pt2- and six equivalent Ag2+ atoms to form distorted AgAg6Pt6 cuboctahedra that share corners with eighteen equivalent AgAg6Pt6 cuboctahedra, edges with six equivalent AgAg6Pt6 cuboctahedra, edges with twelve equivalent PtAg6Pt6 cuboctahedra, faces with eight equivalent AgAg6Pt6 cuboctahedra, and faces with twelve equivalent PtAg6Pt6 cuboctahedra. All Ag–Ag bond lengths are 2.83 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgPt4 by Materials Project

Pt4Ag crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are six inequivalent Pt+0.25- sites. In the first Pt+0.25- site, Pt+0.25- is bonded to nine Pt+0.25- and three equivalent Ag1+ atoms to form PtAg3Pt9 cuboctahedra that share corners with twelve PtAg3Pt9 cuboctahedra, edges with six equivalent AgAg6Pt6 cuboctahedra, edges with eighteen PtAg3Pt9 cuboctahedra, faces with six equivalent AgAg6Pt6 cuboctahedra, and faces with twelve PtAg3Pt9 cuboctahedra. There are six shorter (2.81 Å) and three longer (2.83 Å) Pt–Pt bond lengths. All Pt–Ag bond lengths are 2.89 Å. In the second Pt+0.25- site, Pt+0.25- is bonded to twelve Pt+0.25- atoms to form PtPt12 cuboctahedra that share corners with three equivalent AgAg6Pt6 cuboctahedra, corners with nine PtAg3Pt9 cuboctahedra, edges with three equivalent AgAg6Pt6 cuboctahedra, edges with twenty-one PtAg3Pt9 cuboctahedra, and faces with eighteen PtAg3Pt9 cuboctahedra. There are six shorter (2.81 Å) and three longer (2.83 Å) Pt–Pt bond lengths. In the third Pt+0.25- site, Pt+0.25- is bonded to twelve Pt+0.25- atoms to form PtPt12 cuboctahedra that share corners with three equivalent AgAg6Pt6 cuboctahedra, corners with nine PtAg3Pt9 cuboctahedra, edges with three equivalent AgAg6Pt6 cuboctahedra, edges with twenty-one PtAg3Pt9 cuboctahedra, and faces with eighteen PtAg3Pt9 cuboctahedra. There are six shorter (2.81 Å) and three longer (2.83 Å) Pt–Pt bond lengths. In the fourth Pt+0.25- site, Pt+0.25- is bonded to twelve Pt+0.25- atoms to form PtPt12 cuboctahedra that share corners with three equivalent AgAg6Pt6 cuboctahedra, corners with nine PtPt12 cuboctahedra, edges with three equivalent AgAg6Pt6 cuboctahedra, edges with twenty-one PtPt12 cuboctahedra, and faces with eighteen PtPt12 cuboctahedra. There are six shorter (2.81 Å) and six longer (2.83 Å) Pt–Pt bond lengths. In the fifth Pt+0.25- site, Pt+0.25- is bonded to twelve Pt+0.25- atoms to form PtPt12 cuboctahedra that share corners with three equivalent AgAg6Pt6 cuboctahedra, corners with nine PtPt12 cuboctahedra, edges with three equivalent AgAg6Pt6 cuboctahedra, edges with twenty-one PtPt12 cuboctahedra, and faces with eighteen PtPt12 cuboctahedra. There are six shorter (2.81 Å) and three longer (2.83 Å) Pt–Pt bond lengths. In the sixth Pt+0.25- site, Pt+0.25- is bonded to twelve Pt+0.25- atoms to form PtPt12 cuboctahedra that share corners with three equivalent AgAg6Pt6 cuboctahedra, corners with nine PtAg3Pt9 cuboctahedra, edges with three equivalent AgAg6Pt6 cuboctahedra, edges with twenty-one PtPt12 cuboctahedra, and faces with eighteen PtPt12 cuboctahedra. There are six shorter (2.81 Å) and six longer (2.83 Å) Pt–Pt bond lengths. Ag1+ is bonded to six equivalent Pt+0.25- and six equivalent Ag1+ atoms to form AgAg6Pt6 cuboctahedra that share corners with six PtPt12 cuboctahedra, corners with six equivalent AgAg6Pt6 cuboctahedra, edges with six equivalent AgAg6Pt6 cuboctahedra, edges with eighteen PtPt12 cuboctahedra, faces with six equivalent AgAg6Pt6 cuboctahedra, and faces with twelve equivalent PtAg3Pt9 cuboctahedra. All Ag–Ag bond lengths are 2.81 Å.

36 MATERIALS SCIENCE↗